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Re: [PATCH 3/5] build: arm64: provide -target and -march if using clang
- To: Julien Grall <julien@xxxxxxx>
- From: Luca Fancellu <Luca.Fancellu@xxxxxxx>
- Date: Tue, 3 Dec 2024 10:35:48 +0000
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- Cc: Jan Beulich <jbeulich@xxxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Anthony PERARD <anthony.perard@xxxxxxxxxx>, Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
- Delivery-date: Tue, 03 Dec 2024 10:36:15 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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- Thread-topic: [PATCH 3/5] build: arm64: provide -target and -march if using clang
HI,
> On 2 Dec 2024, at 20:38, Julien Grall <julien@xxxxxxx> wrote:
>
> Hi Jan,
>
> On 02/12/2024 07:52, Jan Beulich wrote:
>> On 30.11.2024 18:15, Julien Grall wrote:
>>> On 29/11/2024 22:12, Volodymyr Babchuk wrote:
>>>> Jan Beulich <jbeulich@xxxxxxxx> writes:
>>>>> On 29.11.2024 02:49, Volodymyr Babchuk wrote:
>>>>>> --- a/config/arm64.mk
>>>>>> +++ b/config/arm64.mk
>>>>>> @@ -5,6 +5,10 @@ CONFIG_XEN_INSTALL_SUFFIX :=
>>>>>> CFLAGS += #-marm -march= -mcpu= etc
>>>>>> +ifeq ($(clang),y)
>>>>>> +CFLAGS += -target aarch64 -march=armv8-a
>>>>>> +endif
>>>>>
>>>>> Why is this dependent on (just?) $(clang), not (also?) $(llvm)?
>>>>
>>>> Because this parameter is handled by clang only. There is no harm in
>>>> providing it explicitly. When building on arm64, value of this parameter
>>>> will match the default value for the platform. When building on x86, we
>>>> need to tell clang that it should generate arm64 code anyways. There is
>>>> no reason in trying to make ARM build with x86 instruction set.
>>>>
>>>>> Also
>>>>> this affects both toolstack builds and hypervisor. Is applying -march
>>>>> like this actually appropriate for the toolstack?
>>>>
>>>> This is a good question. I can't see why this can't be appropriate for
>>>> toolstack. I.e. what bad can happen when building the toolstack.
>>>
>>> In the future, we may want to build the tools for Armv8-M. So I think
>>> the -march should also applies for the toolstack.
>> Perhaps I don't know enough of the Arm world, but: Wouldn't it be possible
>> to build a tool stack suitable for a wide range for Arm64 flavors, while
>> requiring more targeted hypervisor binaries?
>
> Good question. There are some commonnality between ARMv8-M and ARMv8-R but I
> am not sure whether it means we could use -march=armv8-a build and run on
> ARMv8-M. Adding Ayan and Luca.
AFAIK a binary compiled for armv8-a aarch64 will work also on armv8-r aarch64
since they share almost everything apart from some MPU registers,
instead in order to work on armv8-m we might need to pass the appropriate march
Cheers,
Luca
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